MONDAY, Jan. 27, 2014 -- Preschoolers with lots of brothers and sisters seem to develop language skills a bit slower than other kids -- possibly because they get less attention from mom and dad.

But a new study suggests that a "sensitive" older sibling might make up for it.

A number of studies have found that parents with a brood of kids have less time to dedicate to any one child's learning. And some have shown that the younger children in those families tend to have less-developed vocabularies compared to their first-born sibling.

In the new study of 385 preschoolers, researchers found that those from bigger families (at least three kids) did fare a bit worse on a standard vocabulary test. But that gap was erased if a child had an attentive older sibling.

Experts say the findings, reported online Jan. 27 and in the February print issue of Pediatrics, show that it's not only parents who help young children learn.

In studies on child development, "there's a big focus on parents," noted lead researcher Heather Prime, a doctoral student in clinical child psychology at the University of Toronto.

"But there is a place for sibling influences as well," Prime said.

Based on her team's findings, it's a "cognitively sensitive" older sibling who makes a difference. That basically means the older child is in tune with what a young sibling can understand, and changes the way he or she talks to match that -- maybe slowing down or using simpler sentences, but not "baby-talking" them, either.

The findings are based on 385 Ontario families who were part of a larger, long-term study on child development. Researchers followed one child from each family starting at birth.

When those children were 3 years old, the researchers had them play a picture game that measures "receptive" vocabulary -- the words a child understands when other people say them. They also observed the children as they played a structured game with their older sibling, who was about 5 years old, on average.

Overall, the study found, preschoolers from big families tended to score a bit lower on the vocabulary test. And the relationship was still apparent when the researchers weighed other factors -- such as family income, and whether the parents were foreign-born or spoke a language other than English at home.

However, in cases where those kids had a sensitive big brother or sister, the vocabulary disadvantage disappeared.

And it wasn't just because parents were doing something right, because the researchers also measured mothers' cognitive sensitivity in interactions with their children.

"Even controlling for what moms were doing, we still saw the importance of the sibling," Prime said.

"This is a very interesting study," said Diane Paul, director of clinical issues in speech-language pathology for the American Speech-Language-Hearing Association in Rockville, Md. "And the findings make a lot of sense. We know that learning language is a social process."

What's "remarkable," Paul said, is that even kindergarten-age children are able to perceive the needs of a younger sibling and change how they communicate. "It seems like they're helping to create a language-learning environment," she added.

Paul noted that, according to one theory, an older sibling might get in the way of a preschoolers' language development -- by speaking for the younger child, for example. And that might be true in some cases.

But based on these findings, Paul said, a sensitive older sibling may be an asset. She added, though, that this study only looked at one aspect of language development -- receptive vocabulary.

"It would be nice to study other measures, too, like expressive vocabulary," Paul said. Expressive vocabulary refers to the words children not only understand, but use.

And how does a kindergartner become cognitively sensitive to their younger sibling? It's not clear, Prime said. It may be a combination of nature and what they learn from their parents and other people in their lives.

But both Prime and Paul said parents can do things to encourage more-sensitive interactions between their young kids.

An example Prime offered: Five-year-old Johnny and 3-year-old Susie are fighting over a toy. Instead of just saying, "Susie had it first," the parents could encourage Johnny to think about how Susie would feel having that toy taken away from her.

Saying "your sister had it first" may teach a child a rule, Prime noted. But the other approach helps them learn to consider their younger sibling's thoughts and feelings.